tree d24674a1bec6be7d9f97ad845c2a0ad9e7d52f02
parent 88ca67b787a94a729be9cfce29fd831fa5e7b34e
author Boyan Karatotev <boyan.karatotev@arm.com> 1743672579 +0100
committer Varun Wadekar <vwadekar@nvidia.com> 1744319974 +0000

fix(spm-mm): prevent excessive racing

The current code does the following:

sp_state_wait_switch:
	lock()
	if (status == 0)
		status = 1
	unlock()

[critical section]

sp_state_set:
	lock()
	status = 0
	unlock()

One core will obtain the status for itself and then all other cores will
get the lock, see the status is not available, release the lock, and try
again. However, when there are many cores this causes a lot of lock
contention and the original core is racing to obtain the lock to release
the status. This starves the holder of the lock, resulting in an
apparent deadlock, although given enough time it will pass.

Hold the lock throughout to prevent this.

Also make the functions static as they are never exported and drop
sp_state_try_switch() as its unused and would not work anymore.

Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>
Change-Id: Ifa8be75086f2e5b2f8a7c6f266a01dd4deb133e4